Diazotype photoprinting material susceptible to thermal development



United States Patent 3,298,834 DIAZO'IYPE PHOTOPRINTING MATERIAL SUS- CEPTIBLE T0 THERMAL DEVELOPMENT Robert I. Eldred, Jr., Endicott, and John Joseph McKinney, Binghamton, N.Y., assignors to General Aniline & Film Corporation, New York, N .Y., a corporation of Delaware No Drawing. Filed July 1, 1963, Ser. No. 292,098 8 Claims. (Cl. 96-91) This invention relates to an improvement in two-component light-sensitive diazotype photoprinting material susceptible to development by heating.

Two-component diazotype material comprises a supporting sheet, such as paper or film, having in a surface coating or layer, an azo coupling component and a stabilized light-sensitive diazonium compound, stablized against premature coupling by inclusion of an acid stabilizer. On exposure of such coating to actinic light under an opaque pattern on a translucent background, the light-sensitive diazonium compound is destroyed in the light-struck areas, and upon subsequent exposure to an alkaline developing medium such as gaseous ammonia, the acid stabilizer is neutralized and the residual diazonium compound couples with the azo coupling component to form an azo dye image corresponding to the opaque pattern of the original.

It has been proposed to include in two-component light-sensitive diazotype photoprinting material, one or more reagents having an acid to neutral reaction which, on heating, are decomposed or converted to yield an alkaline reacting compound. Diazotype photoprinting material containing such reagents can be developed after exposure to light under an opaque pattern by heating at a temperature causing the aforesaid conversion or decomposition. The alkaline reaction product formed thereby neutralizes the acid stabilizer and causes imagewise coupling of the residual diazonium compound with the azo coupling component.

Incorporation in diazotype materials of various reagents or combination which provide an alkaline environment on heating have been disclosed in the prior art. Thus, United States Patents 2,228,562, 2,681,277, 2,732,- 299 and 2,774,669 disclose two-component diazotype photoprinting material containing nitrogen compounds (eg urea derivatives) which on heating, decompose to form ammonia or nitrogen bases which cause coupling in the two-component diazotype system. U.S.P. 2,653,- 091 discloses inclusion in a two-component diazotype photoprinting layer of trichloroacetic acid as a stabilizer and an alkali metal, ammonium or nitrogen base salt of said acid as a heat sensitive alkali generating compound, said salt being decomposed on heating to yield an alkaline carbonate which promotes coupling.

Acid stabilizers included in two-component diazotype material are usually organic acids such as citric acid, tartaric acid or the like. The stability of the photoprinting material aiforded by such stabilizers tends, how ever, to be reduced by the presence of the neutral to acid reagents which form an alkaline compound upon heating and this causes a critical reduction of the shelf life of the heat developable photoprinting material. While this effect can be reduced by increasing the amount of acid stabilizer, this has the disadvantage of impairing the development properties or requiring increased amounts of the heat-sensitive alkali generating reagents.

We have found that greatly improved shelf life can be obtained in heat developable diazotype photoprinting material of the nature described above, by incorporating ice in the sensitizing solution and consequently in the resultant light-sensitive layer a salt of a naphthalene sulfonic acid having two to three sulfonic acid groups e.g., the

sodium, potassium or ammonium salts of naphthalene-2, 7-disulfonic acid, naphthalene-1,6-disulfonic acid or naphthalene-1,3,6-trisulfonic acid.

The quantity of naphthalene sulfonic acid salt employed is preferably at least 5% of the other non-volatile ingredients of the sensitizing composition. Suitable proportions range up to about 25% of the other non-volatile ingredients of the sensitizing composition. The concentration of the naphthalene sulfonic acid salt in the sensitizing solution generally ranges from 1 to 10% by weight.

The sensitizing compositions of this invention may contain as light-sensitive stable diazonium compounds, those listed in U.S.P. 2,501,874 and in the article by Van der Grinten in the Photographic Journal, volume 92-3 (1952), page 46. They are especially diazonium compounds derived from N-monoand N-disubstituted pphenylenediamines, e.g., the diazotization products of:

N,N-diethyl-p-phenylenediamine N-benzyl-N-ethyl-p-phenylenediamine N-ethyl-p-phenylenediamine N,N-diethyl-2-ethoxy-p-phenylenediamine N-ethyl-2-methyl-p-phenylenediamine N,N-bis-hydroxyethyl-p-phenylenedia-mine N-beta-hydroxyethyl-N-methyl-p-phenylenediamine These compounds are preferably stabilized in the form of their double salts with zinc chloride, tin chloride, cadmium chloride and the like.

Azo coupling components which can be incorporated in the photoprinting materials of the invention are:

2,3-dihydroxynaphthalene 1,8-dihydroxynaphthalene 2-methy1 resorcinol 4,4'-diresorcyl sulfide Resorcinol Octylresorcinol Alpha-resorcylamide 3-methyl-1-phenyl-5 -pyrazolone H-acid 2,3 -dihydroxynaphthalene-6-sulfonic acid 2,5 -xylenol Acid stabilizers against premature coupling of the diazoni-um salt and azo coupling component include citric acid, tartaric acid, and similar acidic reagents.

Heat responsive reagents having an acid to neutral reaction at room temperatures, but which are adapted on heating to temperatures between and 200 C. to yield an alkaline reacting component for neutralization of the acid stabilizer in the light-sensitive photoprinting material of the invention, include the monoalkali metal salts of strong organic acids which are decomposed on heating to form basic compounds, such as the monoalkali metal salts of malonic, maleic or oxalic acids; alkali metal salts of aliphatic mono-carboxylic acids and especially the alkali metal (Na, K) and nitrogen base sats of trichloroacetic acid.

In addition to the foregoing materials, there can also be included reagents commonly employed in diazotype photoprinting materials, for example hygroscopic agent such as glycerin; and wetting agents such as saponin, lauryl sulfate, keryl benzene sulfonate or oleyl-N-methyltaurine.

Moreover, there can be included finely divided or colloidal silica or alumina, aqueous dispersions or colloidal solutions of organic film-forming binders, such as colloidally water-soluble polyvinyl alcohol, methyl cellulose, hydroxy ethyl cellulose, gelatin or the like or latex-like dispersions or resins such as polyvinyl acetate, polyvinyl chloride, polyvinyl chlorideacetate, polyvinylidene chloride, apolyacryl-onitrile or polymethylmethacrylate.

The components of the sensitizing composition are preferably incorporated in a single solution or suspension, and applied in a single coating step to the base. The latter may be paper or film, such as polyethylene-terephthalate (Mylar) and similar plastic materials which are capable of withstanding the elevated development temperatures. However, if desired, the various components of the sensitizing compositions can be applied in successive coatings, one containing for example, the diazonium salt and another, the alkali generating heat-sensitive acid to neutral reagent, the azo coupling component being incorporated in either of the two layers.

Materials coated in accordance with the invention are developed after exposure to actinic light under an opaque pattern by heating at temperatures between 100 and 200 C. or preferably between 120 and 160 C. at which decomposition or conversion of the acid to neutral heat sensitive reagent to an alkaline reacting material occurs, causing coupling of the residual diazonium compound With the azo coupling component in the areas corresponding to the opaque pattern to form an azo dye image thereof.

Diazotype photoprinting materials containing naphthalene sulfonic acid salts in accordance with the present invention are characterized by superior shelf life and stability to decomposition in storage, without impairment of the rate and effectiveness of the heat development.

The invention will be illustrated by the following examples, wherein parts and percentages are by weight, unless otherwise indicated.

Example I The following composition was coated on a paper base sheet and dried:

Citric acid 0.5 Sucrose 5.0 N-ethyl-N-2-hydroxyethyl p aminobenzene diazonium chlorozincate 0.7 2,3-dihydroxynaphthalene-o-sodium sulfonate 3.0

For purposes of comparison, a similar composition from which the naphthalene-1,3,6-trisulfonic acid salt was omitted was also coated on a paper sheet and dried. The dried materials were exposed under an opaque pattern to actinic light, and developed by passing the sheet over a cylinder heated at from 150 to 175 C. Similar development of an azo dye image was obtained with both materials. The two materials were then subjected to forced aging, and again tested as indicated above for making a photoprint of an opaque pattern. The results demonstrated that the material containing the naphthalene-trisulfonic acid salt was characterized by superior shelf life as compared with the material lacking said salt.

Example II The procedures of Example I were repeated, except that for naphthalene-1,3,6-trisodium sulfonate, there was substituted an equal amount of naphthalene-2,7-disodium sulfonate. The results obtained were substantially the same as in the preceding example.

4 Example 111 Paper was coated with the following sensitizing composition:

Finely-divided silica (average particle size; 3-6

microns) gr 4.0 Zinc chloride gr 0.5 Magnesium chloride .gr 0.1 Naphthalene-1,3,6-trisodium sulfonate gr 3.0

The foregoing composition, as well as one in which naphthalene-1,3,6-trisodiurn sulfonate is omitted were tested for photoprinting, and found to give substantially equal results on heat development. After forced aging, it was found that the material containing naphthalenetrisodium sulfonate was characterized by greatly superior shelf life as compared with the composition lacking said ingredient.

Inthe foregoing examples, sodium trichloroacetate can be replaced by the corresponding potassium salts, or by nitrogen base salts, e.g., trichloroacetates of diethanolamine or triethanolamine. Moreover, instead of these compounds, there can be used the monoalkali metal salts of heat decomposable organic acids such as the monoalkali metal salts of oxalic, maleic or malonic acid, as well as other heat-decomposable reagents of neutral to acid reaction mentioned in the discussion preceding the examples.

Instead of naphthalene-1,3, 6-trisodium sulfonate, other alkali metal or ammonium salts of naphthalene-1,3,6- trisulfo acid can be used, as well as corresponding amounts of alkali metal or ammonium salts of other naphthalene diand tri-sulfonic acids. The heat developable two-component diazotype photoprint materials of the invention are characterized in each case by superior shelf life as compared with similar materials lacking the naphthalene dior tri-sulfonic acid salts.

Variations and modifications which will be obvious to those skilled in the art can be made in the foregoing procedures and materials without departing from the scope and spirit of the invention.

We claim:

1. Two-component diazotype photoprinting material susceptible to development on heating, having on a surface of a supporting sheet, a light-sensitive layer containing an azo coupling component, a light-sensitive diazonium compound, an acid stabilizer against premature coupling, a neutral to acid monoalkali metal salt of a strong acid which is decomposed to yield an alkaline reacting compound on heating to a temperature between 100 and 200 C. and a neutral salt of a naphthalene sulfonic acid having the formula:

wherein n is an integer from 2 to 3, amounting to at least 5% by weight of the components of the light-sensitive layer.

2. Diazotype photoprinting material as defined in claim 1 wherein said naphthalene sulfonic acid salt is a member of the group consisting of the sodium, potassium and ammonium salts of naphthalene-1,3,6-trisulfonic acid.

3. Diazotype photoprinting materials as defined in claim 1 wherein said naphthalene sulfonic acid salt is a member of the group consisting of the sodium, potassium and ammonium salts of naphthalene-2,7-disulfonic acid.

4. Diazotype photoprinting material as defined in claim 1, wherein the amount of said naphthalene sulfonic acid salt is from 5 to 25% of the remaining components of the light-sensitive layer.

5. A sensitizing composition for two-component diazotype photoprinting material susceptible to development on heating, containing in an aqueous medium, an azo coupling component, a light-sensitive diazonium compound, an acid stabilizer against premature coupling, a neutral to acid monoalkali metal salt of a strong acid which is decomposed to yield an alkaline reacting compound on heating to a temperature between 100 and 200 C. and at least 1% of a neutral salt of a naphthalenesulfonic acid having the formula:

wherein n is an integer from 2 to 3.

6. A sensitizing composition as defined in claim 5 wherein said naphthalene sulfonic acid salt is a member of the group consisting of the sodium, potassium and ammonium salts of naphthalene-1,3,6-trisulfonic acid.

7. A sensitizing composition as defined in claim 5 wherein said naphthalene sulfonic acid salt is a member of the group consisting of the sodium, potassium and ammonium salts of naphthalene-2,7-disu1fonic acid- S. A sensitizing composition as defined in claim 5 wherein the concentration of said naphthalene sulfonic acid salt is from 1 to 10% by weight.

References Cited by the Examiner UNITED STATES PATENTS 2,65 3,091 9/ 1953 Grieg 9649 2,694.009 1 1/ 1954 Sus 9649 X 2,727,820 12/ 1955' Botkin 964-9 2,732,299 1/ 1956 Morrison 9649 3,102,812 9/ 1963 Welch 9 6- 49 X FOREIGN PATENTS 609,912 3/ 1962 Belgium.

750,080 5/ 1 933 France. 1,249,913 11/ 1962 France.

816,601 7/ 1959 Great Britain.

OTHER REFERENCES Kosar, Photographic Science and Engineering, vol. 5, No. 4, July-August, 196-1, pages 239-243.

I. TRAVIS BROWN, Primary Examiner.

NORMAN G. TORCH'IN, Examiner.

R. L. STONE, Assistant Examiner. 

1. TWO-COMPONENT DIAZOTYPE PHOTOPRINTING MATERIAL SUSCEPTIBLE TO DEVELOPMENT ON HEATING, HAVING ON A SURFACE OF A SUPPORTING SHEET, A LIGHT-SENSITIVE LAYER CONTAINING AN AZO COUPLING COMPONENT, A LIGHT-SENSITIVE DIAZONIUM COMPOUND, AN ACID STABILIZER AGAINST PREMATURE COUPLING, A NEUTRAL TO ACID MONOALKALI METAL SALT OF A STRONG ACID WHICH IS DECOMPOSED TO YIELD AN ALKALINE REACTING COMPOUND ON HEATING TO A TEMPERATURE BETWEEN 100 AND 200*V. AND A NEUTRAL SALT OF A NAPHTHALENE SULFONIC ACID HAVING THE FORMULA: 